Film formation of a water-based paint dispersion occurs from the coalescence of polymer particles. During water evaporation, the polymer particles approach each other, are deformed and polymeric macromolecular chains forming polymeric particles interdiffuse to form ideally continuous dry films. The different steps of the coalescence process are mostly governed by surface tension. The film formation—coalescence of the particles—occurs only if the capillary forces (proportional to the surface tension of the dispersion medium) are higher than the deformation forces (related to the mechanical properties of the polymer) and progress laterally (exterior to interior) and vertically (top to bottom). This particular progression mode promotes the formation of a thin skin of dry polymer on the top of the paint. This thin skin is the origin of the defects appearing during paint application. An increase of the open time of water-based paints could be induced by lowering the surface tension during the coalescence or by other phenomenon slowing down the film formation process.
Paint compositions imparting increased open time are known in the art, for example fluorosurfactant-containing compositions lowering the surface tension. As the fluorine-based surfactants lower the surface tension considerably, foaming and other problems occur such as problems with coalescence and hence film formation.
It would be desirable to provide a dispersion which extends the open time such that paints more conveniently can be applied, in particular in the absence of any other occurring problems such as surface tension decrease and/or foaming problems. The open time is the time available during which the paint can be reworked at a previously painted area. Open time is a key performance property for coatings, particularly for brush applications. Decorative paints can thereby be applied more conveniently and flexibly. Also, it would be desirable to provide a stable paint dispersion. In particular, it would be desirable to provide dispersions which can be easily stored and transported without precipitation or gellation. It would also be desirable to provide a convenient and inexpensive method of producing such a dispersion. An object of the present invention is to provide such a dispersion which simultaneously minimises the environmental impact, for example avoidance of solventborne paints. In addition, it is desirable to maintain or shorten the drying time of the paint after application on a substrate.